296 EXPERIMENTS WITH PLANTS 



of the controls as possible ; on exposing them again 

 to the light, what happens ? 



Temperature, as well as light, plays a part in the 

 process. The Crocus or the Tulip can be made to open 

 or close at any time of day by changing the tem- 

 perature. The experiment should be commenced in the 

 morning before the flower has opened, and the tem- 

 perature should not go above 15° C. On placing it 

 where the temperature is 20° to 25° C. it begins to 

 open: if it be returned to the original temperature it 

 will soon begin to close. In this way it is possible to 

 make it open, close and open again all within an 

 hour.^ 



The flowers of some alpine plants have been ob- 

 served to open and close several times during the 

 course of an hour as they were illuminated or dark- 

 ened by passing clouds. 



The amount of moisture in the air also has some- 

 thing to do with the matter. A flower of the Poor 

 Man's Weather-glass kept in a saturated atmosphere 

 refuses to open even when given the normal amount 

 of illumination. Make experiments on this point. 

 The flowers may float on a cork in a glass jar which 

 is covered with a piece of glass cemented on air-tight 

 with vaseline. (The jar should be large enough so 

 that the flower will not suffer for lack of oxygen : 



» Simply submerging the flower in water which is about 10° C. warmer than 

 the air, will in most cases cause it to open rapidly. 



